JP2009104721A - Ddr memory controller and semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a temporal overhead caused by a change of the operation frequency of a DDR memory. <P>SOLUTION: A DDR memory controller 10 includes a clock control circuit 20 and a strobe delay circuit 40. The clock control circuit 20 outputs any one of a plurality of clock signals CLK1 to CLKn as an operation clock signal SCLK of a DDR memory 1. The strobe delay circuit 40 delays a strobe signal DQS output from the DDR memory 1 by a predetermined delay time tSD. The delay time tSD is adjusted such that a phase of one CLK1 of the plurality of clock signals CLK1-CLKn which has a maximum frequency is shifted by a predetermined angle. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a DDR memory controller for a DDR memory and a semiconductor device on which the DDR memory controller is mounted.

  As a type of SDRAM (Synchronous Dynamic Random Access Memory), DDR (Double Data Rate) -SDRAM capable of high-speed data transfer is known. The DDR-SDRAM is hereinafter referred to as “DDR memory”. The memory controller for the DDR memory is hereinafter referred to as “DDR memory controller”.

  In high-speed data transfer between the DDR memory and the DDR memory controller, a dedicated signal called “strobe signal” is used. Specifically, the data transmission side outputs a strobe signal together with the data signal. The strobe signal repeats the H / L toggle operation at every output timing of the data signal, but is a signal different from the clock signal. The data receiving side takes in the data signal with reference to the received strobe signal instead of the clock signal.

  For example, when reading data, the DDR memory outputs a strobe signal in addition to a data signal indicating read data. The DDR memory controller refers to the received strobe signal and latches the received data signal at the timing of the rising edge and falling edge of the strobe signal. At this time, in order to perform latching in a state where the data signal is stable, the DDR memory controller delays the received strobe signal and latches the data signal with reference to the delayed strobe signal. As a technique for delaying the strobe signal, a technique using a DLL (Delay Locked Loop) circuit and a delay circuit is known (see Patent Document 1 and Non-Patent Document 1).

  FIG. 1 shows FIG. 30 shows a DDR memory controller 140 described in FIG. The DDR memory controller 140 receives a data signal DQ and a strobe signal DQS output from the DDR memory. The data signal DQ is, for example, an 8-bit signal (DQ0 to DQ7). As shown in FIG. 1, the DDR memory controller includes a slave delay circuit 110, a master DLL circuit 120, and a gear ratio logic circuit 130.

  The slave delay circuit 110 is a circuit that delays the strobe signal DQS received from the DDR memory. Specifically, the slave delay circuit 110 includes a variable delay circuit whose number of delay stages changes according to the delay code, and delays the strobe signal DQS by a delay time tSD corresponding to the number of delay stages. With reference to the rising and falling edges of the strobe signal DQS output from the slave delay circuit 110, the flip-flop group latches the data signal DQ. Since data signal DQ is latched in a stable state, the number of delay stages (delay time tSD) is typically set such that the phase of strobe signal DQS is shifted by approximately 90 degrees. In other words, the delay code is determined so that the phase of the strobe signal DQS is shifted by about 90 degrees.

  Here, it is necessary to note that the characteristics of the delay elements constituting the delay circuit change depending on temperature and manufacturing variations. That is, even when the delay code (the number of delay stages) is the same, the delay time tSD may vary depending on temperature and manufacturing variations. In order to align the delay time tSD for each semiconductor chip, it is necessary to adjust (trim) the delay code for each semiconductor chip. A configuration for performing such trimming of the delay code is the master DLL circuit 120 and the gear ratio logic circuit 130.

  The master DLL circuit 120 receives the operation clock CK of the DDR memory as a reference clock, and obtains the number of delay stages such that the phase of the reference clock CK is shifted 360 degrees (one cycle). Specifically, the master DLL circuit 120 includes a variable delay circuit, a phase detector, and a delay controller. The variable delay circuit has the same configuration as the slave delay circuit 110 described above, and the number of delay stages changes according to the control signal output from the delay controller. The variable delay circuit receives the reference clock CK and delays the reference clock CK by a delay time tCK corresponding to the set number of delay stages. The reference clock CK that is not delayed and the delayed reference clock CK that is output from the variable delay circuit are input to the phase detector. Then, the phase detector compares the phases of the two reference clocks CK and outputs the comparison result to the delay controller. The delay controller changes the control signal based on the comparison result, and changes the number of delay stages in the variable delay circuit. With such a configuration, it is possible to determine the number of delay stages such that the reference clock CK is delayed by one cycle.

  The gear ratio logic circuit 130 divides the number of delay stages such that the reference clock CK is delayed by one cycle by “4”. As a result, the number of delay stages is calculated such that the phase of the reference clock CK is shifted by 90 degrees. A signal indicating the calculated number of delay stages is a delay code in the semiconductor chip. The slave delay circuit 110 sets the number of delay stages based on the determined delay code, and delays the strobe signal DQS by the delay time tSD.

  In this manner, the trimming of the delay code is performed for each semiconductor chip by the master DLL circuit 120 and the gear ratio logic circuit 130. As a result, the delay time tSD of the strobe signal DQS in the slave delay circuit 110 is uniform for each semiconductor chip. That is, it becomes possible to cope with the temperature of the operating environment and manufacturing variations.

JP 2004-220463 A DesignLine, Volume 8, Issue 3, 3Q99, Micron Technology Inc.

  In recent years, there is a demand for operating a DDR memory at various operating frequencies. For example, when data is not read out very much, there is a desire to reduce the operating frequency of the DDR memory in order to reduce power consumption. According to the configuration shown in FIG. 1, when the operation clock CK of the DDR memory is changed, the above-described delay code is also set to an appropriate value accordingly. Thereby, even after the operating frequency of the DDR memory is changed, the DDR memory controller can stably capture the data signal DQ.

  However, a certain amount of time is required for resetting (re-trimming) the delay code. Therefore, during the resetting of the delay code, it is necessary to put the DDR memory in a standby state, which reduces the throughput. That is, the time overhead due to the resetting of the delay code accompanying the change in the operating frequency of the DDR memory causes a decrease in throughput.

  [Means for Solving the Problems] will be described below using the numbers and symbols used in [Best Mode for Carrying Out the Invention]. These numbers and symbols are added in parentheses in order to clarify the correspondence between the description of [Claims] and [Best Mode for Carrying Out the Invention]. However, these numbers and symbols should not be used for the interpretation of the technical scope of the invention described in [Claims].

  In the first aspect of the present invention, the strobe signal (DQS) from the DDR memory (1) is delayed by the slave delay (40) based on the delay code (DCODE) determined by the master DLL (50), and the DDR A DDR memory controller (10) is provided which provides a strobe signal (DQS ') for the data signal (DQ) from the memory (1). The DDR memory controller (10) outputs a clock signal (SCLK) selected in response to a frequency selection signal (SEL) from a plurality of clock signals (CLK1 to CLKn) having different frequencies to the DDR memory (1). A circuit (20) is provided. The master DLL (50) receives a clock signal (CLK1) having the maximum frequency among the plurality of clock signals (CLK1 to CLKn) as a reference clock (REF).

  In the second aspect of the present invention, the DDR memory controller (10) includes a clock control circuit (20) and a strobe delay circuit (40). The clock control circuit (20) outputs any one of a plurality of clock signals (CLK1 to CLKn) having different frequencies as an operation clock signal (SCLK) of the DDR memory (1). The strobe delay circuit (40) delays the strobe signal (DQS) output from the DDR memory (1) by a predetermined delay time (tSD). The delay time (tSD) is adjusted to an amount by which the phase of the clock signal (CLK1) having the maximum frequency among the plurality of clock signals (CLK1 to CLKn) is shifted by a predetermined angle.

  In a third aspect of the present invention, a semiconductor device on which the DDR memory controller (10) is mounted is provided.

  According to the present invention, the request to change the operation clock signal (SCLK) of the DDR memory (1) is satisfied by the clock control circuit (20). On the other hand, the delay code (DCODE) is obtained by using the clock signal (CLK1) having the maximum frequency among the plurality of clock signals (CLK1 to CLKn) that can be the operation clock signal (SCLK) of the DDR memory (1) as a reference. It is determined. That is, the delay time (tSD) of the strobe signal (DQS) is an amount by which the phase of the clock signal (CLK1) having the maximum frequency is shifted by a predetermined angle regardless of the operation clock signal (SCLK) of the DDR memory (1). Adjusted.

  Consider a case where the operation clock signal (SCLK) of the DDR memory (1) is changed from the clock signal (CLK1) having the maximum frequency to another one (CLK2 to CLKn). At this time, the setup budget of the data signal (DQ) with respect to the strobe signal (DQS ') does not change, which is not a problem in operation. Further, the hold budget of the data signal (DQ) with respect to the strobe signal (DQS ') inevitably becomes larger, and this also causes no problem in operation. That is, regardless of what clock signal is selected as the operation clock signal (SCLK) of the DDR memory (1), the DDR memory controller (10) can stably capture the data signal (DQ). In other words, even if the operation clock signal (SCLK) of the DDR memory (1) is changed, it is not necessary to trim the delay code (DCODE) again.

  As described above, the reference clock signal (REF) at the time of trimming the delay code (DCODE) is a plurality of clock signals (CLK1 to CLKn) that can be the operation clock signal (SCLK) of the DDR memory (1). Of these, the clock signal (CLK1) having the maximum frequency is fixed. In this case, even if the operation clock signal (SCLK) of the DDR memory (1) is changed, it is not necessary to trim the delay code (DCODE) again. Therefore, the time overhead associated with the change of the operation clock signal (SCLK) is reduced. As a result, a decrease in throughput is prevented and the operation speed is improved as a whole.

  According to the present invention, the time overhead associated with changing the operating frequency of the DDR memory is reduced. As a result, a decrease in throughput is prevented and the operation speed is improved as a whole.

  A DDR memory controller and a semiconductor device according to embodiments of the present invention will be described with reference to the accompanying drawings.

1. 1. First embodiment 1-1. Overall Configuration FIG. 2 is a block diagram showing a configuration of a DDR memory controller and a semiconductor device according to the first embodiment of the present invention. The semiconductor device includes a DDR memory (DDR-SDRAM) 1 and a DDR memory controller 10. For example, the DDR memory 1 and the DDR memory controller 10 are configured as separate semiconductor chips. The DDR memory controller 10 may be mounted on a logic semiconductor chip or the like. That is, a semiconductor integrated circuit on which the DDR memory controller 10 is mounted may be provided. Furthermore, the DDR memory 1 and the DDR memory controller 10 may be configured in one semiconductor chip.

  The DDR memory 1 operates based on the operation clock signal SCLK. At the time of data reading, the DDR memory 1 outputs a strobe signal DQS corresponding to the data signal DQ in addition to the data signal DQ (DQ0 to DQi) indicating the read data.

  The DDR memory controller 10 has a function of outputting the operation clock signal SCLK to the DDR memory 1 and switching the operation clock signal SCLK. Further, the DDR memory controller 10 has a function of receiving the data signal DQ and the strobe signal DQS signal from the DDR memory 1 and outputting the data signal DQ to the outside based on the strobe signal DQS. In order to realize these functions, the DDR memory controller 10 includes a clock control circuit 20, an output circuit 30, a strobe delay circuit 40, and a DLL circuit 50. Hereinafter, each configuration will be described in detail.

1-2. Clock control circuit In recent years, there is a demand for operating the DDR memory 1 at various operating frequencies depending on the situation. That is, there is a demand for dynamically changing the operation clock signal SCLK of the DDR memory 1. A configuration for meeting such a demand is the clock control circuit 20.

  The clock control circuit 20 receives the reference clock signal CLK from the outside of the DDR memory controller 10. Typically, the reference clock signal CLK is a system clock signal. The clock control circuit 20 generates a plurality of clock signals CLK1 to CLKn having different frequencies based on the received reference clock signal CLK (n is an integer of 2 or more). Further, the clock control circuit 20 outputs any one of the generated clock signals CLK <b> 1 to CLKn to the DDR memory 1 as the operation clock signal SCLK of the DDR memory 1.

  More specifically, as shown in FIG. 2, the clock control circuit 20 includes a clock generation circuit 60 and a clock selection circuit 70. The clock generation circuit 60 generates a plurality of clock signals CLK1 to CLKn having different frequencies from the reference clock signal CLK. On the other hand, the clock selection circuit 70 receives the frequency selection signal SEL in addition to the plurality of clock signals CLK1 to CLKn. The frequency selection signal SEL is a signal that specifies the operation clock signal SCLK of the DDR memory 1, and is issued by, for example, the CPU. The clock selection circuit 70 selects one operation clock signal SCLK from the plurality of clock signals CLK1 to CLKn in response to the frequency selection signal SEL, and outputs the selected operation clock signal SCLK to the DDR memory 1.

  Thus, the clock control circuit 20 generates a plurality of clock signals CLK1 to CLKn, and outputs the operation clock signal SCLK selected according to the frequency selection signal SEL to the DDR memory 1. The DDR memory 1 operates based on the selected operation clock signal SCLK, that is, operates based on any one of the plurality of clock signals CLK1 to CLKn. It can be said that the plurality of clock signals CLK <b> 1 to CLKn generated by the clock control circuit 20 are candidates that can be the operation clock signal SCLK of the DDR memory 1.

  FIG. 3 shows an example of the circuit configuration of the clock control circuit 20. In FIG. 3, the clock generation circuit 60 has a plurality of frequency dividing circuits 61, 62 and 63. Each of the frequency dividing circuits 61, 62, and 63 generates clock signals CLK1, CLK2, and CLK3 having different frequencies from the reference clock signal CLK. For example, the frequency dividing circuits 61, 62, and 63 are a 1/2 frequency dividing circuit, a 1/4 frequency dividing circuit, and a 1/8 frequency dividing circuit, respectively. In this case, the frequency of the clock signal CLK1 generated by the frequency dividing circuit 61 is maximized, and the frequency of the clock signal CLK3 generated by the frequency dividing circuit 63 is minimized. As another form of the clock generating circuit 60, a configuration having a buffer through which the input clock (CLK) is passed in addition to the frequency dividing circuits 61, 62, 63 is also possible.

  The clock selection circuit 70 receives the clock signals CLK1 to CLK3 and the frequency selection signal SEL. The frequency selection signal SEL includes a selection signal SEL1 indicating selection / non-selection of the clock signal CLK1, a selection signal SEL2 indicating selection / non-selection of the clock signal CLK2, and a selection signal SEL3 indicating selection / non-selection of the clock signal CLK3. Become. For any selection signal, it is assumed that the H level means “selection” and the L level means “non-selection”. Here, the selection signals SEL1, SEL2, and SEL3 are exclusively set so that one clock signal is selected from the plurality of clock signals (CLK1 to CLK3).

  In FIG. 3, the clock selection circuit 70 has a selection circuit 75 and a synchronization circuit 80. The synchronization circuit 80 is a circuit for synchronizing the frequency selection signal SEL with each of the clock signals CLK1 to CLK3, and includes flip-flop groups 81 to 83. Specifically, the flip-flop group 81 includes flip-flops connected in multiple stages, and synchronizes the selection signal SEL1 using the clock signal CLK1. Similarly, the flip-flop group 82 synchronizes the selection signal SEL2 using the clock signal CLK2, and the flip-flop group 83 synchronizes the selection signal SEL3 using the clock signal CLK3. Although an example in which a decoded signal is input as the selection signal SEL (SEL1 to SEL3) is shown here, the clock selection circuit 70 decodes the selection information and outputs the selection signal SEL (SEL1 to SEL3). You may have a decoding circuit.

  The selection circuit 75 selects and outputs a clock signal corresponding to the frequency selection signal SEL (SEL1 to SEL3) output from the synchronization circuit 80 from the clock signals CLK1 to CLK3. For example, as illustrated in FIG. 3, the selection circuit 75 includes AND circuits 71 to 73 and an OR circuit 74. The AND circuit 71 receives the clock signal CLK1 and the selection signal SEL1 output from the synchronization circuit 80. The AND circuit 72 receives the clock signal CLK2 and the selection signal SEL2 output from the synchronization circuit 80. The AND circuit 73 receives the clock signal CLK3 and the selection signal SEL3 output from the synchronization circuit 80. The outputs of the AND circuits 71 to 73 are input to the OR circuit 74. The signal output from the OR circuit 74 is the operation clock signal SCLK of the DDR memory 1.

  FIG. 4 is a timing chart showing an example of the operation of the clock control circuit 20 shown in FIG. FIG. 4 shows the reference clock signal CLK, the clock signals CLK1 to CLK3, the selection signal SEL1, the output of the AND circuit 71, the selection signal SEL2, the output of the AND circuit 72, and the selected operation clock signal SCLK. Note that the numbers given to the respective stages in FIG. 4 mean the signals at the positions indicated by the corresponding numbers in FIG.

  In the example shown in FIG. 4, only the selection signal SEL1 is initially at the H level, and the other selection signals are at the L level. As a result, the clock control circuit 20 selectively outputs the clock signal CLK1 having the maximum frequency among the clock signals CLK1 to CLK3 as the operation clock signal SCLK. Thereafter, the selection signal SEL1 is changed to L level. Subsequently, the selection signal SEL2 is changed from the L level to the H level. As a result, the clock control circuit 20 selectively outputs the clock signal CLK2 among the clock signals CLK1 to CLK3 as the operation clock signal SCLK. As described above, the operation clock signal SCLK is switched from the clock signal CLK1 having the maximum frequency to the clock signal CLK2 having a lower frequency.

  FIG. 5 shows another example of the circuit configuration of the clock control circuit 20. In FIG. 5, the configuration of the clock selection circuit 70 is the same as that shown in FIG. On the other hand, the clock generation circuit 60 further includes a PLL circuit 64 in addition to the frequency dividing circuits 61 to 63. The PLL circuit 64 has a function of multiplying the frequency of the reference clock signal CLK. In this case, each of the frequency dividing circuits 61 to 63 generates clock signals CLK1 to CLK3 from the multiplied reference clock signal CLK '. Thus, the clock control circuit 20 may generate the plurality of clock signals CLK1 to CLK3 after multiplying the reference clock signal CLK. Even in this case, the role played by the clock control circuit 20 is the same.

1-3. Output Circuit and Strobe Delay Circuit With reference to FIG. 2 again, the output circuit 30 and the strobe delay circuit 40 (slave delay circuit) of the DDR memory controller 10 will be described.

  The strobe signal DQS output from the DDR memory 1 is first input to the strobe delay circuit 40. The strobe delay circuit 40 is a circuit that delays the strobe signal DQS received from the DDR memory 1 by a predetermined delay time (tSD). Specifically, the slave delay circuit 40 includes a variable delay circuit 41 composed of multistage delay elements. The number of stages of the delay elements, that is, the delay time (tSD) changes according to “delay code DCODE” described later. That is, the strobe delay circuit 40 delays the strobe signal DQS by a delay time (tSD) corresponding to the delay code DCODE. The delayed strobe signal DQS is hereinafter referred to as “strobe signal DQS ′”. The strobe signal DQS ′ is supplied to the output circuit 30.

  The output circuit 30 receives the data signal DQ (DQ0 to DQi) output from the DDR memory 1. The data signal DQ is, for example, an 8-bit signal (DQ0 to DQ7). Further, the output circuit 30 receives the strobe signal DQS ′ through the strobe delay circuit 40. Then, the output circuit 30 refers to the received strobe signal DQS 'and takes in the data signal DQ at the timing of the rising edge and the falling edge of the strobe signal DQS'.

  Specifically, as illustrated in FIG. 2, the output circuit 30 includes flip-flops 31-0 to 31-i and flip-flops 32-0 to 32-i. The strobe signal DQS 'is input to the flip-flops 31-0 to 31-i. Then, each of the flip-flops 31-0 to 31-i latches the data signals DQ0 to DQi at the timing of the rising edge of the strobe signal DQS '. On the other hand, an inverted signal of the strobe signal DQS 'is input to the flip-flops 32-0 to 32-i. Each of the flip-flops 32-0 to 32-i latches the data signals DQ0 to DQi at the timing of the falling edge of the strobe signal DQS '. Then, the output circuit 30 outputs the data signals DQ0 to DQi to the outside of the DDR memory controller 10.

  FIG. 6 is a timing chart showing the relationship between the data signal DQ and the strobe signals DQS and DQS '. The DDR memory 1 operates based on the operation clock signal SCLK described above, and outputs a data signal DQ and a strobe signal DQS. At this time, the strobe signal DQS repeats the H / L toggle operation at every output timing of the data signal DQ.

  Within the DDR memory controller 10, the strobe delay circuit 40 delays the strobe signal DQS by a predetermined delay time tSD. As a result, the timing of the rising edge and falling edge of the strobe signal DQS ′ output from the strobe delay circuit 40 includes the data signal DQ in the stable period. That is, a sufficient setup time t (setup) and hold time t (hold) are secured for the data signal DQ. As a result, the output circuit 30 can latch the data signal DQ while the data signal DQ is stable. In FIG. 6, it is described that there is no phase difference (skew) at each edge of the data signal DQ and the strobe signal DQS. However, in practice, as will be described later (for example, FIG. 8), a skew occurs between each data signal DQ and the strobe signal DQS.

  Thus, the strobe delay circuit 40 delays the strobe signal DQS by the delay time tSD, so that the DDR memory controller 10 can latch the data signal DQ in a stable state. In other words, the delay time tSD is set so that the data signal DQ is latched in a stable state. The delay time tSD is determined by the number of stages of delay elements constituting the variable delay circuit 41, and the number of stages is set according to the delay code DCODE.

  Here, it should be noted that the characteristics of the delay element change depending on temperature and manufacturing variations. That is, even when the delay code DCODE (the number of delay stages) is the same, the delay time tSD may vary depending on temperature and manufacturing variations. In order to align the delay time tSD for each semiconductor chip, it is necessary to adjust (trim) the delay code DCODE for each semiconductor chip. A configuration for performing such trimming of the delay code DCODE is a DLL circuit 50 described below.

1-4. DLL Circuit With reference to FIG. 2 again, the DLL circuit 50 (master DLL circuit) will be described. The DLL circuit 50 trims the delay code DCODE that specifies the delay time tSD in the strobe delay circuit 40 (slave delay circuit), and determines an appropriate delay code DCODE.

  In determining the delay code DCODE, the DLL circuit 50 according to the present embodiment uses the “maximum frequency clock signal CLK1” among the plurality of clock signals CLK1 to CLKn generated by the clock control circuit 20 as a reference clock REF. Use. That is, regardless of the operation clock signal SCLK of the DDR memory 1, the DLL circuit 50 determines the delay code DCODE using the clock signal CLK1 having the maximum frequency. For this purpose, the DLL circuit 50 receives the clock signal CLK1 having the maximum frequency from the clock control circuit 20 as the reference clock REF (see FIGS. 2, 3, and 5).

  As shown in FIG. 2, the DLL circuit 50 includes a variable delay circuit 51, a phase detector 52, a delay controller 53, and a code generation logic circuit 54. The variable delay circuit 51 is a replica of the variable delay circuit 41 included in the strobe delay circuit 40, and has multistage delay elements. The number of stages of delay elements (the number of delay stages) varies according to the control signal output from the delay controller 53. The variable delay circuit 51 receives the reference clock REF and delays the reference clock REF by a delay time corresponding to the set number of delay stages.

  The reference clock REF that is not delayed and the delayed reference clock REF that is output from the variable delay circuit 51 are input to the phase detector 52. Then, the phase detector 52 compares the phases of the two reference clocks REF and outputs the comparison result to the delay controller 53. The delay controller 53 changes the control signal based on the comparison result, and changes the number of delay stages in the variable delay circuit 51.

  The variable delay circuit 51, the phase detector 52, and the delay controller 53 described above can determine the number of delay stages such that the phase of the reference clock REF is shifted by 360 degrees (one cycle). The code generation logic circuit 54 is a division circuit that divides the number of delay stages by which the phase of the reference clock REF is shifted by 360 degrees by a predetermined number. For example, the code generation logic circuit 54 divides the number of delay stages by “4”. As a result, the number of delay stages is calculated such that the phase of the reference clock REF is shifted by 90 degrees. In other words, the number of delay stages is calculated such that the phase of the clock signal CLK1 having the maximum frequency is shifted by 90 degrees.

  A signal indicating the number of delay stages calculated in this way is a delay code DCODE. The DLL circuit 50 according to the present embodiment determines the delay code DCODE so that the phase of the clock signal CLK1 having the maximum frequency is shifted by a predetermined angle (for example, 90 degrees). The above strobe delay circuit 40 sets the number of delay stages based on the determined delay code DCODE, and delays the strobe signal DQS by the delay time tSD. That is, the delay time tSD of the strobe signal DQS is adjusted (trimmed) so that the phase of the clock signal CLK1 having the maximum frequency is shifted by a predetermined angle (for example, 90 degrees).

  As described above, according to the present embodiment, the reference clock REF input to the DLL circuit 50 is fixed to the clock signal CLK1 having the maximum frequency regardless of the operation clock signal SCLK of the DDR memory 1. . In other words, the delay code DCODE is determined by using the clock signal CLK1 having the maximum frequency among the clock signals CLK1 to CLKn that can be the operation clock signal SCLK as a reference. As a result, the delay time tSD of the strobe signal DQS is adjusted to an amount by which the phase of the clock signal CLK1 having the maximum frequency is shifted by a predetermined angle without depending on the operation clock signal SCLK. Note that even if the operation clock signal SCLK of the DDR memory 1 is changed, the delay code DCODE and the delay time tSD do not change.

1-5. Switching of Operation Clock Signal of DDR Memory Next, the operation of the DDR memory controller 10 when the operation clock signal SCLK of the DDR memory 1 is switched will be described. FIG. 7 is a timing chart showing an example of the switching process of the operation clock signal SCLK. FIG. 7 shows a command for the DDR memory 1, an operation clock signal SCLK, a strobe signal DQS and data signal DQ output from the DDR memory 1, and a strobe signal DQS ′ output from the strobe delay circuit 40.

  In the example shown in FIG. 7, a read command (READ) is input to the DDR memory 1, and then a no operation command (NOP) is input. In response to the read command (READ), the DDR memory 1 reads data. At this time, the burst length is assumed to be 8.

  Initially, the operation clock signal SCLK of the DDR memory 1 is the clock signal CLK1 having the maximum frequency. The DDR memory 1 outputs a strobe signal DQS and a data signal DQ based on the clock signal CLK1 having the maximum frequency. The strobe signal DQS and the data signal DQ are output during the NOP command period. In the DDR memory controller 10, the strobe delay circuit 40 delays the strobe signal DQS by a predetermined delay time tSD. The delay time tSD is set to an amount by which the phase of the clock signal CLK1 having the maximum frequency is shifted by a predetermined angle.

  At a certain timing during the period of the NOP command, the frequency selection signal SEL is changed and the operation clock signal SCLK is switched. For example, the operation clock signal SCLK is switched from the clock signal CLK1 having the maximum frequency to the lower clock signal CLK2 (see FIG. 4 described above). As shown in FIG. 4 and FIG. 7, the operation clock signal SCLK changes to the clock signal CLK2 after a while from the clock signal CLK1. Thereafter, the DDR memory 1 outputs a strobe signal DQS and a data signal DQ based on the clock signal CLK2.

  It should be noted that the reference clock REF input to the DLL circuit 50 remains the clock signal CLK1 having the maximum frequency. In other words, the delay code DCODE is not re-trimmed in the DLL circuit 50, and the delay code DCODE remains constant. Therefore, the delay time tSD of the strobe signal DQS by the strobe delay circuit 40 does not change. The delay time tSD remains the amount by which the phase of the clock signal CLK1 with the maximum frequency is shifted by a predetermined angle.

  FIG. 8 conceptually shows timing budgets when the operating frequency of the DDR memory 1 is the maximum frequency and in other cases. More specifically, FIG. 8 shows a strobe signal DQS and a data signal DQ input to the DDR memory controller 10. The strobe signal DQS reaches the DDR memory controller 10 at time t1. In consideration of the skew, the period during which the data signal DQ is stable is a period indicated by “Data Valid” in the drawing. It is desirable that the edge timing of the strobe signal DQS 'is located at time t2 within the stable period of the data signal DQ. A difference between the time t2 and the time t1 is a desirable delay time tSD. However, in an actual delay circuit, an error may occur in the delay time tSD. In consideration of such uncertainty (SU), a setup budget and a hold budget can be defined as shown in FIG.

  As described above, according to the present embodiment, the delay code DCODE is trimmed by using the clock signal CLK1 having the maximum frequency. That is, the delay time tSD is set so that the setup / hold constraint is satisfied even when the operating frequency of the DDR memory 1 is maximum.

  Next, consider a case where the operating frequency is other than the maximum frequency. Also in this case, the delay code DCODE, that is, the delay time tSD is the same as in the case of the maximum frequency. Therefore, the setup budget is not different from the case of the maximum frequency, but this is not a problem in operation. On the other hand, as shown in FIG. 8, the hold budget is inevitably larger than the maximum frequency. Of course, there is no problem in operation. That is, since a timing budget at least equivalent to that of the maximum frequency is ensured, normal operation is ensured.

  As described above, a sufficient timing budget is ensured regardless of what clock signal is selected as the operation clock signal SCLK of the DDR memory 1, so that the DDR memory controller 10 can stably capture the data signal DQ. is there. In other words, since a sufficient timing budget is guaranteed, there is no need to trim the delay code DCODE again even if the operation clock signal SCLK is changed.

  As described above, the delay code DCODE is determined by using the clock signal CLK1 having the maximum frequency among candidates that can be the operation clock signal SCLK of the DDR memory 1. In this case, even if the operation clock signal SCLK of the DDR memory 1 is changed, it is not necessary to trim the delay code DCODE again. Therefore, it is not necessary to put the DDR memory 1 in the standby state during the re-trimming process of the delay code DCODE in the DDR memory controller 10. When the frequency selection signal SEL is switched, the DDR memory 1 can operate immediately without waiting for a re-trimming process on the controller side. Thus, the time overhead associated with the dynamic change of the operation clock signal SCLK is reduced. As a result, a decrease in throughput is prevented and the operation speed is improved as a whole.

  Note that the switching timing of the operation clock signal SCLK is not limited to the example shown in FIG. The switching timing of the operation clock signal SCLK may be appropriately determined according to the specifications on the DDR memory 1 side. For example, consider a case where the specification of the DDR memory 1 permits switching of the operation clock signal SCLK during the self-refresh operation. In that case, as shown in FIG. 9, the operation clock signal SCLK may be switched during the self-refresh operation. Even in the case of the example shown in FIG. 9, the processing on the DDR controller 10 side is the same. That is, the DDR controller 10 according to the present embodiment can be applied universally regardless of the specifications on the DDR memory 1 side.

1-6. Effect According to the present embodiment, a request to dynamically change the operation clock signal SCLK of the DDR memory 1 is satisfied by the clock control circuit 20.

  Further, the reference clock REF used when the delay code DCODE is trimmed is fixed to the clock signal CLK1 having the maximum frequency among the plurality of clock signals CLK1 to CLKn that can be the operation clock signal SCLK of the DDR memory 1. In this case, even if the operation clock signal SCLK of the DDR memory 1 is changed, it is not necessary to trim the delay code DCODE again. Therefore, the time overhead associated with the dynamic change of the operation clock signal SCLK is reduced. As a result, a decrease in throughput is prevented and the operation speed is improved as a whole.

2. Second Embodiment FIG. 10 is a block diagram showing a configuration of a DDR memory controller and a semiconductor device according to a second embodiment of the present invention. The semiconductor device includes a DDR memory 1 and a DDR memory controller 10. In the present embodiment, the DDR memory controller 10 has a holding circuit 90 in addition to the configuration shown in FIG. Other configurations are the same as those in the first embodiment, and redundant description is omitted as appropriate.

  The holding circuit 90 is a storage circuit that holds the delay code DCODE, and is connected to the DLL circuit 50 and the strobe delay circuit 40. The DLL circuit 50 outputs the determined delay code DCODE to the holding circuit 90, and the holding circuit 90 holds the delay code DCODE determined by the DLL circuit 50. The delay code DCODE is output from the holding circuit 90 to the strobe delay circuit 40. The strobe delay circuit 40 delays the strobe signal DQS based on the delay code DCODE held by the holding circuit 90.

  As described in the first embodiment, even if the operation clock SCLK of the DDR memory 1 is changed, it is not necessary to perform trimming of the delay code DCODE again. Therefore, once the delay code DCODE is determined, the operation of the DLL circuit 50 can be stopped. Thereby, power consumption is reduced.

  For example, when the DDR memory controller 10 is initialized, the enable signal EN is set to H level, and the DLL circuit 50 determines the delay code DCODE. After the delay code DCODE is determined, the enable signal EN is set to the L level, and the DLL circuit 50 is set to the standby state. Thereby, the toggle operation of the reference clock REF in the DLL circuit 50 is eliminated, and the power consumption is greatly reduced. Even when the DLL circuit 50 is in the standby state, the delay code DCODE is output from the holding circuit 90 to the strobe delay circuit 40, so that the strobe delay circuit 40 can delay the strobe signal DQS.

3. Other Examples The present invention is not limited to the description of any of the above embodiments. For example, each of the variable delay circuits 41 and 51 described above has a multi-stage delay element having a fixed number of stages, and the operating voltage (power supply voltage) of the delay element changes according to a control signal output from the delay controller 53. It is good also as a structure. For example, if the variable delay circuit 51 is composed of four stages of delay elements, the delay elements can shift the phase by 90 degrees for each stage.

  In any of the above-described embodiments, the clock generation circuit 60 is shown. In the case where a plurality of clocks having different frequencies can be separately prepared for the DDR controller of the present invention, it is needless to say that a configuration in which a plurality of clock signals having different frequencies are directly input to the clock selection circuit 70 may be adopted.

  Furthermore, the semiconductor device provided with the DDR memory 1 and the DDR controller 10 described above may be simply mounted as an independent semiconductor integrated circuit (semiconductor chip) on a printed board (PCB). Alternatively, as a SIP (System In Package), a DDR memory chip and a semiconductor chip on which the DDR controller 10 is mounted may be housed in one semiconductor package substrate. A semiconductor chip on which the DDR memory chip or the DDR controller 10 is mounted may be mounted in a desired number (one or more).

FIG. 1 is a block diagram showing a configuration of a DDR memory controller in the prior art. FIG. 2 is a block diagram showing the configurations of the DDR memory controller and the semiconductor device according to the first embodiment of the present invention. FIG. 3 is a circuit diagram showing an example of the configuration of the clock control circuit. FIG. 4 is a timing chart showing an example of the operation of the clock control circuit. FIG. 5 is a circuit diagram showing another example of the configuration of the clock control circuit. FIG. 6 is a timing chart showing the relationship between the data signal DQ and the strobe signals DQS and DQS '. FIG. 7 is a timing chart showing an example of the operation clock signal switching process of the DDR memory. FIG. 8 is a conceptual diagram showing a comparison of timing budgets in the case of the highest frequency and other frequencies. FIG. 9 is a timing chart showing another example of the operation clock signal switching process of the DDR memory. FIG. 10 is a block diagram showing a configuration of a DDR memory controller and a semiconductor device according to the second embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DDR memory 10 DDR memory controller 20 Clock control circuit 30 Output circuit 40 Strobe delay circuit 41 Variable delay circuit 50 DLL circuit 51 Variable delay circuit 52 Phase detector 53 Delay controller 54 Code generation logic circuit 60 Clock generation circuit 61-63 Frequency division Circuit 64 PLL circuit 70 Clock selection circuit 75 Selection circuit 80 Synchronization circuit 90 Holding circuit CLK Reference clock signal CLK1 to CLKn Clock signal SCLK Operation clock signal DQ Data signal DQS, DQS 'Strobe signal REF Reference clock SEL Frequency selection signal DCODE Delay code

Claims (14)

A DDR memory controller that delays a strobe signal from a DDR memory by a slave delay based on a delay code determined by a master DLL, and sets a strobe signal for a data signal from the DDR memory;
A clock control circuit that outputs a clock signal selected according to a frequency selection signal from a plurality of clock signals having different frequencies to the DDR memory;
A DDR memory controller, wherein a clock signal having a maximum frequency among the plurality of clock signals is input to the master DLL as a reference clock. The DDR memory controller according to claim 1,
The DDR memory controller, wherein the clock control circuit includes a clock generation circuit that generates the plurality of clock signals from an input reference clock signal. The DDR memory controller according to claim 2,
The clock control circuit further includes a clock selection circuit that selects a clock signal corresponding to the frequency selection signal from the plurality of clock signals and outputs the selected clock signal to the DDR memory. Memory controller. The DDR memory controller according to claim 2,
The clock control circuit includes:
A plurality of frequency dividers for generating each of the plurality of clock signals from the reference clock signal;
A synchronization circuit for synchronizing the frequency selection signal to each of the plurality of clock signals;
A DDR memory controller, comprising: a selection circuit that selects, from the plurality of clock signals, a clock signal corresponding to the frequency selection signal output from the synchronization circuit. A DDR memory controller according to any one of claims 2 to 4,
The DDR memory controller, wherein the clock control circuit includes a PLL circuit that multiplies the frequency of the reference clock signal, and the plurality of clock signals are generated from the multiplied reference clock signal. A DDR memory controller according to any one of claims 1 to 5,
The DDR memory controller, wherein the delay code is determined at initialization and does not change even when a clock signal output to the DDR memory changes. A clock control circuit that outputs any one of a plurality of clock signals having different frequencies as an operation clock signal of the DDR memory;
A strobe delay circuit for delaying a strobe signal output from the DDR memory by a predetermined delay time;
The delay time is adjusted to an amount by which a phase of a clock signal having a maximum frequency among the plurality of clock signals is shifted by a predetermined angle. DDR memory controller. The DDR memory controller according to claim 7,
The clock control circuit includes a clock generation circuit that generates the plurality of clock signals from an input reference clock signal. DDR memory controller. A DDR memory controller according to claim 7 or 8,
And a DLL circuit for receiving the clock signal having the maximum frequency from the clock control circuit.
The DLL circuit determines a delay code in which the phase of the clock signal having the maximum frequency is shifted by the predetermined angle,
The strobe delay circuit delays the strobe signal by the delay time based on the delay code. DDR memory controller. A DDR memory controller according to claim 9,
Furthermore, it has a holding circuit for holding the delay code,
The strobe delay circuit delays the strobe signal based on the delay code held by the holding circuit. DDR memory controller. A DDR memory controller according to claim 10,
The DLL circuit determines the delay code at initialization, and is set to a standby state after the delay code is determined. DDR memory controller. The DDR memory controller according to any one of claims 7 to 11,
The clock control circuit includes a clock selection circuit that selects the operation clock signal from the plurality of clock signals in response to a frequency selection signal and outputs the selected operation clock signal to the DDR memory.   A semiconductor integrated circuit comprising the DDR memory controller according to claim 1. DDR memory,
A DDR memory controller,
The DDR memory controller
A clock control circuit that outputs any one of a plurality of clock signals having different frequencies as an operation clock signal of the DDR memory;
A strobe delay circuit for delaying a strobe signal output from the DDR memory by a predetermined delay time;
The delay time is adjusted to an amount by which a phase of a clock signal having a maximum frequency among the plurality of clock signals is shifted by a predetermined angle.

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